1. Field of the Invention
The invention relates generally to a method of manufacturing a transistor in a semiconductor device. More particularly, the invention relates to a method of manufacturing a transistor in a semiconductor device capable of lowering the threshold voltage by implementing a surface channel CMOS device both in the NMOS region and the PMOS region, in such a way that a Ta film or a TaNx film is formed at a low temperature or a first TaNx film in which the composition(x) of nitrogen is 0.45xcx9c0.55 is formed, on a gate insulating film in a NMOS region, so that the work function becomes 4.0xcx9c4.4 eV, and a Ta film or a TaNx film is formed at a high temperature or a second TaNx film in which the composition(x) of nitrogen is 0.6xcx9c1.4 is formed, on a gate insulating film in a PMOS region, so that the work function becomes 4.8xcx9c5.2 eV.
2. Description of the Prior Art
In semiconductor devices, a silicon oxide film (SiO2) is mainly used as a gate insulating film in DRAMs and logic devices. As the design rule is reduced, there is a trend that the thickness of the silicon oxide film is reduced below 25xcx9c30 xc3x85, which is a tunneling limit.
In case of below 0.1 xcexcm DRAM, it is expected that the thickness of the gate insulating film will be about 30xcx9c35 xc3x85. In case of logic devices, on the other hand, it is expected that the thickness of the gate dielectric film will be about 13xcx9c15 xc3x85. When the gate electrode is formed of polysilicon, however, as the thickness of the gate insulating film increased electrically by means of a depletion phenomenon of polysilicon is about 3xcx9c8 xc3x85, there is a significant obstacle in reducing the thickness (Teff) of the effective gate insulating film with about 15xcx9c30 xc3x85. Therefore, as one solution to overcome this, a study has recently been made in which a high dielectric constant material is used as a gate insulating film. Meanwhile, there is a study in which the gate electrode is formed of a metal instead of polysilicon in order to minimize the depletion phenomenon of polysilicon.
Also, a lot of studies has recently been made in which the gate electrode is formed of a metal since it can prevent the problem of boron penetration, which is generated when the gate electrode is formed of polysilicon and a junction region is formed using a p-type impurity, for example, boron.
In order to form the gate electrode with a metal, there has been a lot of studies on TiN or WN. However, as they has the work function of 4.75xcx9c4.85 eV, the work function is formed near the valence band in the mid-gap work function. It could be said that the work function is an adequate level in case of a surface channel PMOS. In case of NMOS, however, if the channel doping is 2xcx9c5xc3x971017/cm3 the threshold voltage is almost 0.8xcx9c1.2 V. In other words, in this case, it could not meet the threshold voltage target of 0.3xcx9c0.6 V, that is required in high-performance devices having low voltage or low power characteristic. Therefore, in order to obtain a low threshold voltage of about 0.3xcx9c0.6 V both in a NMOS and a PMOS, it is preferred that a dual metal electrode having the work function of about 4.0xcx9c4.4 eV in case of NMOS and a dual metal electrode having the work function of about 4.8xcx9c5.2 eV in case of PMOS are used.
It is therefore an object of the present invention to provide a method of manufacturing a transistor in a semiconductor device capable of solving the above problem, by forming a metal gate electrode that has a low work function in a NMOS region but has a high work function in a PMOS region.
Another object of the present invention is to provide a method of manufacturing a transistor in a semiconductor device by which a metal gate electrode having a dual work function is formed by using the fact that the work function of a Ta film or a TaNx film is changed depending on the deposition temperature.
Still another object of the present invention is to provide a method of manufacturing a transistor in a semiconductor device by which a metal gate electrode having a dual work function is formed by using the fact that the work function of a TaNx film is changed depending on the composition of nitrogen.
In order to accomplish the above object, a method of manufacturing a transistor in a semiconductor device according to a first embodiment of the present invention is characterized in that it comprises the steps of injecting each of first impurity and second impurities into given regions of a semiconductor substrate to define a first region and a second region; forming a gate insulating film on the semiconductor substrate in which the first region and the second region are defined; forming a first Ta film having a first work function on the first region; forming a second Ta film having a second work function on the second region; forming a metal layer on the entire structure including the first and second Ta films; patterning the metal layer, the first and second Ta films, and the gate insulating film to form gate electrodes in the first and second regions, respectively; and forming a first junction region by injecting a first impurity into the semiconductor substrate in the first region and forming a second junction region by injecting a second impurity into the semiconductor substrate in the second region.
Also, a method of manufacturing a transistor in a semiconductor device according to a second embodiment of the present invention is characterized in that it comprises the steps of injecting each of first impurity and second impurities into given regions of a semiconductor substrate to define a first region and a second region; forming a gate insulating film on the semiconductor substrate in which the first region and the second region are defined; forming a first Ta film having a first nitrogen composition on the first region so that the first Ta film have a first work function; forming a second Ta film having a second nitrogen composition on the second region so that the second Ta film have a second work function; forming a metal layer on the entire structure including the first and second TaNx films; patterning the metal layer, the first and second TaNx films, and the gate insulating film to form gate electrodes in the first and second regions, respectively; and forming a first junction region by injecting a first impurity into the semiconductor substrate in the first region and forming a second junction region by injecting a second impurity into the semiconductor substrate in the second region.